I'm going at midnight tonight. I'm a huge X-Men fan, and although strongly disliking X3 and Wolverine, the early word on this is very promising. James McAvoy and Michael Fassbender are terrific actors and a truly audacious choice for the roles. I can't wait. I'll report back with my findings.
Edit:
I'm exhausted but I have to say that the film was spectacular. I always ranked X2 alongside The Dark Knight as my favorite modern superhero/comic films (not including stuff like The Incredibles, which wasn't a comic) but I truly believe First Class to be better than X2.
The characters are beautifully drawn, the plotting is intelligent, the action is exciting and filled with character and emotion, and the performances are great. Fassbender and McAvoy are legendary.
I'll update this tomorrow with more thoughts but for now I'll just say... wow.